This from Samantha E. Weissbluth writing for Wealth Management:
In a recent New York case, a father, in his will, dictated that his gay son’s child get nothing unless his son married the child’s mother. Manhattan resident Frank Mandelbaum founded the ID verification company, Inteli-Check, and

Let’s say you got a divorce. As part of the divorce agreement your ex agreed to leave half of his estate to your kids. He dies. He leaves a will that doesn’t comply with the agreement – leaving 90% of his estate to his second wife. What happens? Enforce the contract you say, the kids get half. That’s what you and I think the answer should be. Maybe you have a divorce settlement with a similar provision. Will it hold up? That is the issue that has been tying up the Oleg Cassini estate for years.
The October 29, 2008 edition of Trust & Estates contains this article:
Jerry Orbach’s son, Chris, says his stepmother, Elaine Cancilla-Orbach is a "double-dealing, lying, scheming, miserable fool." All he got from his dad’s estate was "a few CD’s, two sweaters, a pool cue and a pocketknife."